1. Field of the Invention
This invention relates to a remotely operated tool for making and breaking the threaded connection between a drill head and a stabilizer mounted on the end of a drill string.
2. Description of the Related Art
Raise boring is a method of underground rock drilling used in the mining industry. This method involves drilling a pilot hole from one level of a mine to a lower level, removing the pilot bit, attaching a larger diameter raise boring head to the drill string and pulling it back through the previously drilled pilot hole. Finally, the raise boring head is lowered back down to the lower level, where the raise boring head is removed from the drill string.
Typically, the drill string is composed of a plurality of pipe sections which are secured to each other by threaded connections. The drill string typically terminates at a stabilizer unit, to which is connected the pilot bit during the first phase of the operation, and the raise boring head during subsequent phases of the raise boring operation. The threaded connections within the drill string are designed to transmit the "working torque" load between the drilling rig on the upper mine level and the pilot drill or raise boring head. However, the connections must be preloaded at a torque up to approximately 20% greater than the working torque. All of the connections within the drill string are preloaded by the drilling rig, except for the connection between the stabilizer and the raise boring head.
Detaching the pilot drilling head, and attaching and detaching the raise boring head involves the use of torque tools to "break" and "make" the rotary shouldered threaded connections between the respective heads and the stabilizer. These torque tools are also used to generate the necessary pre-loading torque. Various torque tools have been developed for this purpose. See, for example, Canadian Patents Nos. 910,895; 927,374; 929,510; 988,502; 1,004,215; 1,009,225; 1,112,683; and Canadian Patent Application No. 2,156,560 (published May 19, 1996). These references describe respective systems for making and breaking the joint between pipe sections of a drill string, and are also usable for making and breaking the joint between the drill head and the stabilizer unit at the end of the drill string.
However, as demonstrated by the systems taught by the above references, known torque tools require that at least a portion of the mechanism surrounds the drill string. Thus in each case, the torque tools must be installed around the drill string prior to use. Problems which exist with this installation are generally safety issues. Primarily, the torque tool equipment is heavy and working conditions often make it awkward and unsafe for men to work. Once the raise boring operation is complete, the raise boring head must be detached from the drill string, and this typically requires that workers must stand on the raise boring head to attach the torque tools, thereby exposing the men to the dangers associated with working under the open hole. In order to alleviate these problems, additional equipment can be installed to protect the men from falling rock. However, these measures are expensive and time consuming.
An object of the present invention is to provide a method and apparatus for making and breaking the threaded connection between a drill head and a stabilizer mounted on the end of a drill string, which overcomes the above-noted deficiencies of the prior art.
Another object of the invention is to provide a method and apparatus for making and breaking the threaded connection between a drill head and a stabilizer mounted on the end of a drill string, such that the need for men to work under an open hole is substantially eliminated.